The new St Peter's still wasn't finished when Pope Gregory XIII started building this pontifical summer palace on the highest of Rome's seven hills; begun in 1573, the Quirinale was not completed until over 200 years later. The risk that a pontiff (not, on the whole, renowned for youthful vigour) might keel over during the holidays was such that it was decided to build somewhere suitable to hold a conclave to elect a successor. The Quirinale's Cappella Paolina (named after Paul V) was designed by Carlo Maderno and finished in 1617; it is a faithful replica of the Vatican's Sistine Chapel, minus the Michelangelos. Accommodation for the cardinals was provided in the Manica lunga, the immensely long wing that runs the length of via del Quirinale to the rear of the palace. Bernini added the main entrance door in 1638.
On Sunday mornings, when parts of the palace are open to the public, you may be lucky enough to catch one of the noon concerts held in the chapel. The presidential guard changes with a flourish each afternoon outside on the square at any time between 3pm and 6pm, depending on the season.